Dehydrodithizone and mercaptotetrazolium salts as silver halide photographic antifoggants and stabilizers



United States Patent 3,420,664 DEHYDRODITHIZONE AND MERCAPTOTETRA-ZOLIUM SALTS AS SILVER HALIDE PHOTO- GRAPHIC ANTIFOGGANTS ANDSTABILIZERS Fritz Dersch and John A. Welsh, Binghamton, N.Y., assignorsto GAF Corporation, a corporation of Delaware No Drawing. Filed Jan. 3,1966, Ser. No. 517,976 US. Cl. 96-665 10 Claims Int. Cl. G03c 1/34; 1/28ABSTRACT OF THE DESCLOSURE Stabilizer and antifogging compounds for usein silver halide photography include dehydrodithizone and chloride,bromide and iodide salts for S-alkyl m.ercapto-2,3- diaryltetrazole,5-alkyl-mercapto-2,3 dialkyltetrazole,5-carboXyalkylmercapto-2,3-diaryltetrazole and5-carboxyalkylmercapto-Z,3-dialkyltetrazole compounds.

This invention relates in general tophotography and in particular to theprovision of novel stabilizing compounds for use in connection with thepreparation and/ or processing of photographic silver halide emulsions.

It is well known that light-sensitive materials such as gelatin-silverhalide emulsions exhibit a marked tendency to fog. The term fog as usedin the photographic art connotes that portion of the density obtainedupon development which arises by virtue of factors other than thephotographic exposure. The fog may be attributable to a number ofinfluences including for example, excessive ripening of the emulsion,prolonged storage of the film and especially under conditions ofelevated temperature and/ or humidity, as well as by prolongeddevelopment of the exposed emulsion and the like. In general, the fogmay be of two types, namely, yellow fog and chemical (gray) fog. Theyellow fog, sometimes referred to as colored or dichroic fog, isessentially a colloidal deposit of silver, the color intensity andgeneral appearance of which are determined by the minute particle sizeand degree of subdivision. The fog is chiefly yellow in color and ismost apparent in the lighter portions of the negative. The color mayvary, however, and the colloidal silver particles may, for example,appear green by reflected light and yellow or red by transmitted light.

On the other hand, the so-called chemical fog, or gray fog, is the morecommon and is formed in a number of ways. As mentioned hereinbefore,such fog may be caused by the nucleation of silver on or in the silverhalide grains due to inadvertent exposure, excessive ripening of theemulsion, storage of the film under severe conditions of temperatureand/or humidity, etc. Fog may also be caused by exposure to chemicals,for example, hydrogen sulfide and other reactive sulphur compounds,hydrogen peroxide vapors and strongly reducing materials such as thosepresent in the developer solution. In any event, and irrespective of thecause, the fog will usually manifest itself as a spurious density extantover the entire area of the sensitive coating and typically, issubstantially nonuniform.

To overcome or otherwise alleviate the aforedescribed disadvantages ithas become a recognized practice in the photographic art to add certainchemical stabilizer compounds to the light-sensitive emulsion at somestage of its preparation which purportedly function to enhance theirphotographic stability to an appreciable extent. However, in the vastmajority of instances, the stabilizing and antifogging compoundsheretofore employed for such purposes have provided only marginalimprovement since they are often characterized by the disadvantage thatupon addition to the emulsion they cause a loss of speed and/or contrastof the emulsion or otherwise deleteriously affect its sensitometriccharacteristics. The loss in speed is particularly pronounced in thoseregions of the spectrum to which the emulsions are optically or dyesensitized.

In accordance with the discovery forming the basis of the presentinvention, it has been found that the antifogging and stabilizationcharacteristics of light-sensitive silver halide emulsions can besynergistically modified to advantage by the utilization of a particularclass of chemical compounds in connection with the preparation and/orprocessing of such emulsions.

Thus, a primary object of the present invention resides in the provisionof improved antifogging and stabilizer compounds in which the foregoingand related disadvantages are eliminated or at least mitigated to asubstantial degree.

Another object of the present invention resides in the provision oflight-sensitive silver halide emulsions containing a compound whichstabilizes the emulsion against fogging while exhibiting little, if any,tendency to reduce the speed or contrast of such emulsions.

A further object of the present invention resides in the provision oflight-sensitive silver halide emulsions and photographic elementsprepared therewith containing an antifogging compound which issubstantially devoid of any tendency to reduce the sensitivity of theemulsion to light of longer wave length due to the presence of one ormore sensiizing dyes.

A still further object of the present invention resides in the provisionof a process for the treatment of an exposed photographic silver halideemulsion wherein at least one of the steps of pretreating or developingthe emulsion is effected in the presence of a novel stabilizing compoundto be more fully described hereinafter.

The attainment of the foregoing and related objects is made inaccordance with the broader aspects of the present invention by theincorporation in a light-sensitive photographic element, e.g., silverhalide emulsion, developing solution and/or pretreatment solution of acompound selected from the group consisting of (a)S-alkylmercapto-Z,3-diaryltetrazolium salts, (b)5-alkylmercapto-Z,3-dialkyltetrazolium salts, (c)5-carboxyalkylmercapto-Z,3-diaryltetrazolium salts, (d)S-carboxyalkylmercapto-Z,3-dialkyltetrazolium salts and (e)dehydrodithizone.

The compounds encompassed by (a), (b), (c), and (d) can, forconvenience, be represented according to the following structuralformulae:

wherein R, R and R represent alkyl, e.g., methyl, ethyl, propyl,isopropyl, butyl, isobutyl, amyl, hexyl, undecyl, dodecyl, etc., andpreferably lower alkyl of 1 to 4 carbon atoms; aryl, e. g., phenyl,naphthyl which may further contain inert substituents such as amino,hydroxy, alkoxy, acyl, acylamino and the like; R represents loweralkylene, branch or straight chained, substituted or unsubstituted,e.g., methylene, ethylene, isobutylene, etc.; X represents an anion suchas a halide atom, e.g., chloride, bromide or iodide, and M representshydrogen or a watersolubilizing cation such as alkali metal, e.g.,sodium, potassium, etc.; ammonium, substituted ammonium, etc.

The compounds encompassed by each of the above formulae can be preparedaccording to techniques which are well known in the art. In thisconnection, reference is made to the syntheses described in Journal ofthe American Chemical Society, vol. 83, pp. 5023 to 5026; andDissertation, John Reinheimer, The Johns Hopkins University, 1948.

The compound dehydrodithizone as reported in the literature is capableof several formulistic definitions. In this connection specificreference is made to J.A.C.S., vol. 83, p. 5023. Despite the fact thatseveral theories are postulated in explanation of the validity of agiven structural representation, it is nevertheless manifest that theterm dehydrodithizone connotes a specific species of tetrazolium salts.

Improved fog reduction and other beneficial effects are obtained whenthe aforementioned compounds are incorporated into the silver halideemulsion as ripening finals or as coating finals. As is well known,ripening finals are added during the ripening or sensitivity increasingstage of the emulsion making process. Such additions may be effectedbefore, during or after the decomposition of the soluble silver saltsuch as silver nitrate by means of a soluble halide such as potassiumbromide, sodium chloride or the like in the presence of a suitablecolloid carrier such as gelatin, polyvinyl alcohol, solubilized caseinalbumen or the like.

Coating finals are added to the emulsion just prior to coating on asuitable support such as glass, paper or film at a time when theemulsion has nearly attained its maximum sensitivity.

It will also be understood that the novel stabilizers of the presentinvention may be incorporated in a layer adjacent to the sensitizedlayer such as an anti-abrasion layer. The stabilizing compound may beutilized in concentrations varying over a relatively wide range; forexample, when added to the light-sensitive silver halide emulsion layeras a ripening final, it is found that optimum realization of resultsprovided herein are assured with stabilizer concentrations ranging fromas low as .02 milligram up to about 500 milligrams per 0.6 mole ofsilver halide. The concentration selected within the aforestated rangewill depend to a large extent on the type of emulsion employed and thusit is advisable to determine the optimum concentration from case tocase. If added during the emulsion preparation stage, stabilizerconcentrations on the order of approximately one-tenth of those employedwhen adding the stabilizer as a coating final are found to be quitesuitable.

The stabilizer compounds contemplated herein can be applied in a varietyof ways to impart stability to photographic elements. As previouslymentioned, they may be included as a constituent of the emulsion layer,of a surface layer over the emulsion or alternatively, over the base orsupport.

Further embodiments of the present invention contemplate the addition ofsuch compounds to at least one of the developing, fixing, washing,drying, etc. solutions utilized in the processing of the exposedemulsion. For example, when utilized in the Washing step the stabilizercan be applied to the otherwise finished photographic element byimmersing same in an alcohol, e.g., methanol or alcohol-water solutionin the case of the free acid derivatives while the salt derivatives maybe employed effectively as simple water solutions.

In general, it is found that the improvements provided by the presentinvention are particularly manifest according to procedures wherebydevelopment is effected in the presence of said stabilizer compounds.This, of course, would be the case should the stabilizer be included inthe light-sensitive photographic element, the developing solution and/orsuitable developer pre-bath. In any event, when incorporated into thephotographic developer or other processing bath, the stabilizers of thepresent invention are preferably employed in concentrations ranging fromabout 1 to about 50 milligrams per liter of solution, with a range ofabout 5 milligrams to about 20 milligrams per liter being particularlypreferred.

In addition to being useful in orthochromatic and panchromaticemulsions, the stabilizers may also be used in non-sensitized emulsions,X-ray emulsions, paper emulsions, color emulsions and the like. If usedwith sensitizing dyes, they may be added'to the emulsion before or afterdye addition. Moreover, the present stabilizers may also be employed inconjunction with other known antifoggants and stabilizers, reductionstabilizers, metal and noble metal sensitizers or in combination withother additive agents and the like.

The stabilizer may also be employed in gelatin or other water-permeablecolloids including polyamides or a mixture of gelatin with a polyamideas described in U.S. Patent 2,289,775; polyvinyl alcohol and gellingcompound as described in U.S. Patent 2,249,537; polyvinyl acetaldehydeacetal resins and partially hydrolyzed acetate resins described in U.S.Patents 1,939,422 and 2,036,092; cellulose derivatives, e.g., cellulosenitrate, cellulose acetate, and the lower fatty acid esters of celluloseincluding sample and mixed esters and ethers of cellulose and the like.

When preparing the photographic emulsion in accordance with the presentinvention, a solution of the stabilizer in a suitable solvent, such aswater, alcohol, dimethyl formamide or alcohol-water mixture adjusted toa neutral or slightly alkaline pH, i.e. about 7.5 to 10, is made up andthe solution mixed with the emulsion at any convenient stage during itspreparation, but preferably during ripening or just prior to coating.

Although any of the aforedescribed compounds may be utilized toadvantage in the practice of the present invention, particularlybeneficial results are obtained and especially with regard to thesuppression of fog which would otherwise result from film storage undersevere conditions of humidity and temperature with the 1,3-diphenylderivatives. As particular examples of such compounds there may bementioned without limitation the following:

5-methylmercapto-3,3-diphenyltetrazolium iodide5-ethylmercapto-2,3-diphenyltetrazolium iodide5-carboxymethylmercapto-2,3-diphenyltetrazoliurn iodide5-carboxyethylmercapto-2,3-diphenyltetrazolium iodide The followingexamples are given for purposes of illustration only and are not to beconsidered in any way as being limitative of the present invention.

EXAMPLE I (A) Preparation of 5 methylmercapto-2,3-diphenyltetrazoliumiodide.A solution was prepared consisting of dehydrodithizone (1.90 g.)and methyl iodide (1.26 g.) in 100 ml. dry chloroform. The solution thusprepared is refluxed in a 250 ml. flask on a steam bath forapproximately minutes. The solvents are then distilled off to give adark red oil which yields 2.67 g. of solid upon addition of anhydrousether. After crystallization with a mixture comprising cc. isopropanoland 4 cc. of water, the solid obtained had a melting point of 219 C.

Analysis.-Calc. for C H N SI. Calc.: C, 42.4; H, 3.3; S, 8.1, Found: C,42.05, 41.78; H, 3.45, 3.51; S, 7.90, 8.04.

(B) A silver halide emulsion in gelatin containing 2% silver iodide and98% silver bromide is prepared in conventional manner and brought up toits maximum light sensitivity. It is then readied for coating; finalsare added such as sensitizing dyes and hardening agents. Approximately 6cc. of a 0.01% solution of S-methylmercapto- 2,3-diphenyltetrazoliumiodide was added to the emulsion as an antifoggant and stabilizer. Theemulsion samples contained about 0.6 mole of silver halide. The soprepared emulsion samples were then coated on a suitable cellulose esterbase and dried. Samples of these film coatings were then exposed in aType IB sensitometer and developed in a developer of the followingcomposition:

Metol gram 1.5 Sodium sulfite, anhydrous do 45 Sodium bisulfite do 1Hydroquinone do 3 Sodium carbonate, monohydrated do 6 Potassium bromidedo 0.8

Water to make 1 liter.

Quantity of Fog at 12 Oven fog Relative speed Compound Used dev. at 3dev. at 3 dev.

EXAMPLE II (A) Synthesis of Dehydrdithizone.A solution was preparedconsisting of:

K Fe(CN) g 16 Na CO g 15 water .m1 195 95% ethanol ml 223 The solutionthus prepared was added to a one-liter, 3 neck flask equipped with astirrer, condenser, and gas inlet. The air in the flask was thenevacuated and replaced with nitrogen whereupon 6.35 g. ofdiphenylthiocarbazone was added to the flask solution with stirring.Stirring is maintained at room temperature for approximately 48 hourswhereupon there was obtained 5.3 g. of a dark solid which was filteredand washed with a cold water/ethanol solution. After twocrystallizations with ethanol, the product obtained in the form ofbright orange crystals, had a melting point of 180 C.

Analyris.C H N S. Calc.: C, 61.6; H, 3.9. Found: C, 61.19, 61.03; H,4.14, 3.88.

(B) Part B of Example I was repeated except that the5-methylmercapto-2,3-diphenyltetrazolium iodide is replaced in the sameamount with 0.001% solution of dehydrodithizone. After processing thefollowing sensitometric results were obtained:

Quantity of Fog at 12 Oven fog Relative speed Compound Used dev. at 3'dev. at 3' dev.

0 27 24 100 0.02 mg. per kilo 24 .21 100 0.08 mg .22 .17 92 EXAMPLE IIIA silver halide emulsion in gelatin containing 2% silver iodide and 98%silver bromide was coated onto a film base in a manner known to the art.After coating, a solution containing 20' grams of gelatin in 1 liter ofH 0 to which had been added approximately 8 cc. of a 0.001% solution ofdehydrodithizone was coated thereon as an anti-abrasion layer. Afterdrying, the film samples were exposed and processed as described inExample I.

Quantity of Fog at 12 Oven fog Relative speed Compound Used dev. at 3dev. at 3 dev.

5-carboxyethylmercapto-2,3-diphenyltetrazolium chloride5-ethylmercapto-2,3-diphenyltetrazolium iodideS-propylmercapto-Z,3-diphenyltetrazolium iodide5-isobutylmercapto-2,3-diphenyltetrazolium iodide5-carboxypropylmercapto-2,3-diphenyltetrazolium chloride etc.

The developer composition may be any of those conventionally employed inthe development of exposed silver halide emulsions and accordingly, maybe of the hydroquinone type, i.e., those which contain hydroquinone,potassium meta'bisulfite and potassium bromide, or they may be of themetol-hydroquinone type, i.e., those which contain p-methylaminophenol,sodium sulfite, sodium bisulfite, hydroquinone sodium carbonate, andpotassium bromide. Alternatively, the developer composition may be ofthe so-called borax type, i.e., those which contain p-methylaminophenol,sodium sulfite, hydroquinone borax and potassium bromide.

It will also be understood that the novel stabilizers of the presentinvention may be employed singly or in admixtures comprising two or moreof such compounds. Again, optimum combinations thereof can be readilyascertained in a particular instance by routine laboratoryexperimentation.

The present invention has been disclosed with respect to certainpreferred embodiments thereof, and there will become obvious to personsskilled in the art various modifications, equivalents, or variationsthereof which are intended to be included within the spirit and scopethereof.

What is claimed is:

1. A process of treating an exposed silver halide emulsion whichcomprises developing said emulsion in the presence of an antifoggant andstabilizer comprising a compound selected from the group consisting of(a) dehydrodithizone, (b) 5-alkylmercapto-2,3-diaryltetrazoliurnchlorides, bromides and iodides, (c) S-alkylmercapto-2,3-dialkyltetrazolium chlorides, bromides and iodides, (d)S-carboxyalkylmercapto-2,3-diaryltetrazolium chlorides, bromides andiodides, (e) S-carboxyalkylmercapto- 2,3-dialkyltetrazolium chlorides,bromides and iodides and (f) the alkali metal, ammonium and substitutedammonium salts of the carboxy compounds of (d) and (e).

2. A process according to claim 1 wherein said antifoggant andstabilizer compound comprises S-methylmercapto-2,3-diphenyltetrazoliumiodide.

3. A process according to claim 1 wherein said antifoggant andstabilizer compound comprises dehydrodithizone.

4. An aqueous developer solution containing a silver halide photographicdeveloping agent and an antifoggant and stabilizer comprising a compoundselected from the group consisting of (a) dehydrodithizone, (b)5-alkylmercapto-2,3 -diaryltetrazolium chlorides, bromides and iodides,(c) 5-alkylrnercapto-2,3-dialky1tetrazolium chlorides, bromides andiodides, (d) S-carboxyalkylmercapto- 2,3-diaryltetrazolium chlorides,bromides and iodides, (e) 5-carboxyalkylmercapto-Z,3-dia1kyltetrazoliumchlorides, bromides and iodides and (f) the alkali metal, ammonium andsubstituted ammonium salts of the carboxy compounds of (d) and (e).

5. A light-sensitive silver halide emulsion containing an antifoggantand stabilizer comprising a compound selected from the group consistingof (a) dehydrodithizone, (b) 5-alkylmercapto-Z,3-diaryltetrazoliumchlorides, bromides and iodides, (c)5-alky1mercapto-2,3-dialkyltetrazolium chlorides, bromides and iodides,(d) S-carboxyalkylmercapto 2,3 diaryltetrazolium chlorides, bromides andiodides, (e) 5-carboxyalkylmercapt0-2,3-dialkyltetrazolium chlorides,bromides and iodides and (f) the alkali metal, ammonium and substitutedammonium salts of the carboxy compounds of (d) and (e).

6. A light-sensitive silver halide emulsion according to claim 5 whereinsaid antifoggant comprises S-methylmercapto-2,3-diphenyltetrazoliumiodide.

7. A light-sensitive silver halide emulsion according to claim 5 whereinsaid antifoggant comprises dehydrodithizone.

8. A light-sensitive photographic material comprising a base and alight-sensitive silver halide emulsion, said lightsensitive materialcontaining an antifoggant and stabilizer comprising a compound selectedfrom the group consisting of (a) dehydrodithizone, (b) 5-alkylmercapto-2,3-diaryltetrazolium chlorides, bromides and iodides, (c)5-alkylmercapto-2,3-dialkyltetrazolium chlorides, bromides and iodides,(d) S-carboxyalkylrnercapto-2,3-diaryltetrazolium chlorides, bromidesand iodides, (e) 5-carboXya1kylmercapto-2,3-dialkyltetrazoliumchlorides, bromides and iodides and (f) the alkali metal, ammonium andsubstituted ammonium salts of the carboxy compounds of (d) and (e).

References Cited UNITED STATES PATENTS 4/1961 Dersch et al. 96109 1/1963Dersch et al 96-109 3/1967 Willems et al 9629 FOREIGN PATENTS 5/1967Germany.

NORMAN G. TORCHIN, Primary Examiner.

C. E. DAVIS, Assistant Examiner.

U.S. Cl. X.R.

